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bug#15533: optimizing away noticeable effects
From: |
Ian Price |
Subject: |
bug#15533: optimizing away noticeable effects |
Date: |
Tue, 08 Oct 2013 18:13:05 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.1 (gnu/linux) |
Ian Price <address@hidden> writes:
> Does it make sense to add it to find-definition? or should we add it
> before the use in that case?
I've decided that it does, and I've made the following (tentative)
change on my own guile install.
(cond
((lookup (lexical-ref-gensym x))
=> (lambda (op)
- (let ((y (or (operand-residual-value op)
- (visit-operand op counter 'value 10 10)
- (operand-source op))))
- (cond
- ((and (lexical-ref? y)
- (= (lexical-refcount (lexical-ref-gensym x)) 1))
- ;; X is a simple alias for Y. Recurse, regardless of
- ;; the number of aliases we were expecting.
- (find-definition y n-aliases))
- ((= (lexical-refcount (lexical-ref-gensym x)) n-aliases)
- ;; We found a definition that is aliased the right
- ;; number of times. We still recurse in case it is a
- ;; lexical.
- (values (find-definition y 1)
- op))
- (else
- ;; We can't account for our aliases.
- (values #f #f))))))
+ (if (var-set? (operand-var op))
+ (values #f #f)
+
+ ;; var-set? (operand-var ) => #f #f ?
+ (let ((y (or (operand-residual-value op)
+ (visit-operand op counter 'value 10 10)
+ (operand-source op))))
+ (cond
+ ((and (lexical-ref? y)
+ (= (lexical-refcount (lexical-ref-gensym x)) 1))
+ ;; X is a simple alias for Y. Recurse, regardless of
+ ;; the number of aliases we were expecting.
+ (find-definition y n-aliases))
+ ((= (lexical-refcount (lexical-ref-gensym x)) n-aliases)
+ ;; We found a definition that is aliased the right
+ ;; number of times. We still recurse in case it is a
+ ;; lexical.
+ (values (find-definition y 1)
+ op))
+ (else
+ ;; We can't account for our aliases.
+ (values #f #f)))))))
It's a little invasive because of the 'if', but the meat of it is
+ (if (var-set? (operand-var op))
+ (values #f #f)
The check for mutability needs to come before the let, since that's
where we do the lookup for a value, so it would be too late.
If Andy is happy with this change, I'll add a test, and push a commit,
but I'm going leave it to his discretion.
--
Ian Price -- shift-reset.com
"Programming is like pinball. The reward for doing it well is
the opportunity to do it again" - from "The Wizardy Compiled"